last time step headers

[bradduthie]

There really should be column headers in the last time step individual-level CSV files. The columns can be worked out by looking at the code, but I don't think that people should be expected to do this. The tricky bit is that there will need to be some kind of clever way to assign the headers based on the model parameter values, but this shouldn't be too difficult. The first 100 or so columns are the same, and the rest just depend on the genome structure. This can be done in R first before any of the printing in C.